It is known that sheet metal strips which pass out of a rolling mill exhibit defects of surface planarity which essentially arise from the fact that the fibers do not all have the same length. A planing operation consists in deforming the strip in order to stretch the shortest fibers until they have the same length as the longest fibers. In order to ensure that no residual stress remains within the strip, the entire thickness of the sheet metal has to be subjected to plastic deformation. This plastic deformation is produced by subjecting the strip to a combination of tensile stress and alternate bending stresses.
A large number of existing machines permit the achievement of this result, in the first place by passing the strip through small-diameter rolls and subjecting them to a series of successive bending movements in opposite directions and in the second place by passing them through rolls of increasing diameter in order to eliminate the so-called "tile effect". This effect is observed when a strip has been subjected to a series of bending movements or flexural deformations and the tractive force is then released, whereupon the edges of the strip exhibit a tendency to lift with respect to its central portion.
These known machines are usually of complex design since they make use of a large number of rolls (it is worthy of note in this connection that one working roll is usually associated with two backing rolls). The substantial floor space thus required constitutes a prime factor in the introduction of a continuous production line for processing sheet metal strip such as, for example, a galvanizing line. Furthermore, the adjustment of these machines is a very difficult procedure since it entails a sequence of operations at many different points of the machine when changing either the thickness or the width of the strip to be processed. In consequence, these known machines are integrated in continuous strip-processing lines only when these lines are intended to be employed for uniform and large-scale production. At the present time, however, it is observed that this type of mass production no longer corresponds to current requirements of manufacturers who now find that, for reasons of economic performance, low costs and reduced capital outlay, it is preferable to have installations which offer greater adaptability and thus readily permit the possibility of changing from one type of product to another.
French patent No. FR-1,372,009 discloses a machine for planing under tension in which two planing rolls and one tile-correcting roll cooperate with a backup roll. The structural design of this machine does not permit maximum reduction of floor space occupied in the direction of travel of the metal stock.
The object of the present invention is to propose a planing device of much more compact design which not only satisfies the current requirement of adaptability but can also be readily integrated in existing sheet metal rolling-mill lines of the skin-pass type or of the Sendzimir multiroll type.